1. Field of the Invention
The present invention generally relates to a power supply apparatus for use with a television receiver, a monitor or the like, for example. More particularly, this invention relates to a power supply apparatus comprising a main power supply section for rectifying a voltage in either a full-wave rectification fashion or a voltage-doubler rectification fashion in response to a voltage supplied from a commercial alternating-current power supply and a standby power supply section for rectifying a voltage of a commercial alternating-current (hereinafter simply referred to as an AC) in which a full-wave rectification and a voltage-doubler rectification may be switched by detecting rectified outputted voltages from the standby power supply section and the main power supply section.
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows an arrangement of a related-art power supply apparatus for use with a television receiver, a monitor or the like. A power supply apparatus 200, generally depicted by reference numeral 200 in FIG. 1 can be used in the area in which a voltage of a AC power supply is 100V and in the area in which a voltage of a AC power supply is 220V.
As shown in FIG. 1, in the power supply apparatus 200, one end of a AC power supply 1 may be connected to one input terminal of a bridge-type rectifier 2. The other end of this AC power supply 1 may be connected to the other input terminal of the bridge-type rectifier 2 through a contact 3a of a relay 3. The relay 3 may be adapted to supply or to interrupt the AC power supply 1. A relay drive circuit 3D which may drive the relay 3 may be driven under control of a power supply control signal (hereinafter simply referred to as xe2x80x9cCPWxe2x80x9d) supplied from a control section (not shown). When the signal CPW is held at high level, the relay 3 may be driven to close the contact 3a thereby to supply the voltage of the AC power supply 1.
When a contact 7a of a relay 7 is opened, the voltage of the AC power supply 1 may be rectified by the bridge-type rectifier 2 in a full-wave rectification fashion. Then, a DC voltage smoothed by capacitors 4 and 5 connected in series may be inputted to a main DC/DC converter 6. Also, when the contact 7a of the relay 7 is closed, a DC voltage (hereinafter simply referred to as a DC voltage) which was smoothed by the capacitor 4 after it had been rectified by one diode of the bridge-type rectifier 2 and a DC voltage smoothed by the capacitor 5 after it had been rectified by another one diode of the bridge-type rectifier 2 may be added and a voltage-doubler rectification can be performed. The main DC/DC converter 6 may convert the supplied DC voltage into DC voltages of a variety of voltages necessary for a television, a monitor or the like, for example.
The voltage from the AC power supply 1 may be rectified/smoothed by a diode 8 and a capacitor 9 and then inputted to a standby DC/DC converter 10. This standby DC/DC converter 10 may supply a DC voltage necessary for maintaining functions of the control section, the relay drive, the voltage detection circuit or the like when the main DC/DC converter 6 is disabled.
A voltage detection circuit 11 may compare a voltage Vs rectified/smoothed by the diode 8 and the capacitor 9 with a predetermined threshold voltage. The voltage detection circuit 11 may output a detection output (hereinafter simply referred to as xe2x80x9cVDExe2x80x9d) which goes to low level when the voltage Vs is higher than the predetermined threshold voltage and which goes to high level when the voltage Vs is lower than the predetermined threshold voltage. The voltage detection circuit 11 may have a hysteresis characteristic in which a high threshold voltage may be set to DC225V and a low threshold voltage may be set to DC190V, for example. The output VDE may be supplied to a relay drive circuit 7D as a control signal. When the output VDE is held at high level, the relay drive circuit 7D may drive the relay 7 to close: a relay contact 7a, whereby a voltage-doubler rectification can be performed.
FIG. 2 shows an example of an arrangement of this voltage detection circuit 11 more concretely. As shown in FIG. 2, a voltage Vcc applied to a power supply terminal 51 may be supplied through a resistor R7 to a shunt regulator IC2 which may be used to generate a reference voltage. A series circuit of resistors R8 and R9 may be connected to the shunt regulator IC2 in parallel. A voltage developed at a junction between the resistors R8 and R9 may be supplied to the shunt regulator IC2. The shunt regulator IC2 may increase or decrease a current flowing thereto such that the above-mentioned voltage may become constant. Thus, a predetermined reference voltage Vrf may be developed at the junction between the resistors R7 and R8.
As shown in FIG. 2, a voltage Vs may be supplied to a detection voltage input terminal 53 as a detection voltage. A voltage Va that was voltage-divided by resistors R5 and R6 may be supplied to a negative input terminal of a comparator IC1. The reference voltaege Vrf may be supplied through a resistor R4 to a positive input terminal of the comparator IC1. The resistors R3 and R4 may be give a hysteresis characteristic to the comparator IC1, and a diode D2 may be used in order to block a reverse current.
An output terminal of the comparator IC1 may be connected to the base of a transistor Q1, and a bias may be applied to the base of the transistor Q1 from the resistors R1 and R2. The collector of the transistor Q1 may be connected through a coil 7b of the relay 7 to the power supply terminal 51. A diode D1 which is connected in parallel to the coil 7b may be used to suppress the collector voltage of the transistor Q1 from increasing due to a back electromotive force generated in the relay 7 when the transistor Q1 is turned off.
When the voltage of the AC power supply 1 is low (e.g. 100V), accordingly, the detection voltage Vs is low, the voltage Va supplied to the negative input terminal of the comparator IC1 may become lower than the voltage supplied to its positive input terminal so that the output VDE of the comparator IC1 goes to high level. At that very moment, since the transistor Q1 is turned on to drive the relay 7, the contact 7a of the relay 7 may be closed, whereby the voltage-doubler rectification operation can be performed.
When on the other hand the voltage of the AC power supply 1 is high (e.g. 200V), accordingly, the detection voltage Vs is high, the voltage Va supplied to the negative input terminal of the comparator IC1 becomes higher than the voltage supplied to its positive input terminal so that the output VDE of the comparator IC1 goes to low level. At that very moment, since the transistor Q1 is turned off and the relay 7 may not be driven, the full-wave rectification operation may be performed.
When the AC voltage is fluctuated suddenly, in particular, a voltage rises or when a power failure of a short period of time occurs or when a relay drive circuit is operated abnormally, it is unavoidable that the main DC/DC converter is considerably affected by a resultant stress.
It is an object of the present invention to provide a reliable power supply apparatus in which the aforementioned problem can be obviated.
According to the present invention, there is provided a power supply apparatus which is comprised of a main power supply section including a rectifying circuit supplied with a AC voltage through a first or second contact, the rectifying circuit for rectifying the AC voltage in a full-wave rectification fashion or in a voltage-doubler rectification fashion, a standby power supply section including a rectifying circuit for rectifying the AC voltage, a first voltage detection section for detecting whether the rectified output from the standby power supply section is higher than or lower than a predetermined threshold voltage, a second voltage detection section for detecting whether the rectified output from the main power supply section is higher than or lower than a predetermined threshold voltage, and a switch control section for closing any one of the first and second contacts based on a detection signal from the first voltage detection section and a detection signal from the second voltage detection section.
The main power supply section rectifies the AC power supply voltage supplied thereto through the first contact in a full-wave rectification fashion when the voltage of the AC power supply is high, and rectifies the AC power supply voltage supplied thereto through the second contact in a voltage-doubler rectification fashion when the voltage of the AC power supply is low. Control for opening and closing the first and second contacts may be executed by comparing the rectified voltage of the standby power supply and the rectified voltage of the main power supply with a predetermined voltage. Although the voltage change which was started on the rectified half-wave side can be detected by detecting the rectified voltage of the standby power supply, the voltage change which was started on the half-wave side which is not rectified cannot be detected by detecting the rectified voltage of the standby power supply. There is then the possibility that the detection will be delayed until the next half-wave is rectified. By detecting the rectified voltage of the standby power supply together with the rectified voltage of the main power supply, it is possible to provide a highly-reliable power supply apparatus in which the above-mentioned possibility can be obviated.
For example, the first and second voltage detection sections may comprise a comparator for comparing a first voltage corresponding to a threshold voltage and a second voltage corresponding to the rectified output and a charge and discharge circuit inserted into this comparator at its input side of the second voltage. A discharge time constant of the charge and discharge circuit may be made larger than a charge time constant thereof. Thus, under the state that the output level of the comparator selects the full-wave rectification, when a power failure of a short period of time occurs in the AC power supply, an output from the charge and discharge circuit is lowered slowly as compared with the case in which the second voltage is lowered. Hence, the output level of the comparator can be maintained in the state in which such output level selects the full-wave rectification. Thus, when the power failure is ended, the voltage-doubler rectification is not executed and the main DC/DC converter 6 can be protected.
Further, according to the present invention, there is provided a power supply apparatus which is comprised of a main power supply section including a rectifying circuit supplied with a AC voltage through a contact of a first relay or a contact of a second relay, the rectifying circuit for rectifying the AC voltage in a full-wave rectification fashion or a voltage-doubler rectification fashion, a standby power supply section for obtaining a standby power from the AC voltage, a voltage detection section for detecting whether a voltage of the AC voltage is higher than or lower than a predetermined threshold voltage, a first relay drive section for driving the first relay, a second relay drive section for driving the second relay, a switch control section for controlling operations of the first relay drive section and the second relay drive section based on the detected signal from the voltage detection section such that any one of the contact of the first relay and the contact of the second relay is turned on, a switch section for supplying a power source voltage obtained at the standby power supply section to the first relay drive section and the second relay drive section and a power supply on-off control section for controlling on-off of the switch section based on a power supply on-off control signal.
According to this invention, the main power supply section rectifies the AC power supply voltage supplied thereto through the contact of the first relay in a full-wave rectification fashion, and rectifies the AC power supply voltage supplied thereto through the contact of the second relay in a voltage-doubler rectification fashion. In this case, when the voltage of the AC power supply voltage is low, the contact of the second relay is closed such that the voltage-doubler rectification can be executed. When on the other hand the voltage of the AC power supply voltage is high, the contact of the first relay is closed so that the full-wave rectification can be executed.
Control operations for opening and closing the contacts of the first and second relays may be executed by controlling the first and second relay drive sections, respectively, based on the voltage detection signal of the standby power supply rectified output and the voltage detection signal of the main power supply rectified output. The power supply voltage may be supplied to the first and second relay drive sections from the standby power supply through the switch section. When the switch section is opened, the power supply voltage is not supplied to the first and second relay drive sections. Thus, both of the contacts of the first and second relays are turned off, thereby resulting AC voltage is not supplied to the main power supply. When on the other hand the switch section is closed, the power supply voltage is supplied to the first and second relay drive sections so that the contact of the first or second relay is closed based on the voltage detection signal, thereby resulting AC voltage is supplied to the main power supply.
As described above, since the contacts of the first and second relays may be served as also the power supply switch so that the voltage-doubler rectification operation, for example, is effected, only the second relay can be energized. Thus, a power consumption can be decreased.
For example, the power supply apparatus according to the present invention may further include an abnormal voltage detection section for detecting whether the rectified output from the main power supply section is higher than or lower than a predetermined threshold voltage. The power supply on-off control section may control on-off of the switch section based on a detection signal from the abnormal voltage detection section in addition to the power supply on-off control signal. Thus, when the contact of the second relay is closed due to an abnormal operation of the second relay drive section or the like so that an abnormally-high voltage is generated as a rectified output, the supply of power to the second relay is interrupted by de-energizing the switch section based on the detection signal from the abnormal voltage detection section. Thus, a rectified output voltage can be lowered, thereby resulting the main DC/DC converter 6 can be protected.